Maleficent has the power to transform into a monstrous dragon, one that is fought as a boss in several games. She first accesses this form after Riku unlocks her heart in Kingdom Hearts, also using her dragon form to battle Sora and Riku in Kingdom Hearts: Chain of Memories. In Kingdom Hearts Birth by Sleep, she transforms into the dragon in order to stop Aqua and Prince Phillip.
Before this fight, swap out Goofy for Beast, and have Sora's item slots filled with Megalixirs, Ethers and Mega-Potions. Have Aerora and Cura in his magic shortcuts, and keep the abilities Strike Raid and Ars Arcanum on hand. Enter the portal that Maleficent left behind. Heal if necessary.
It is then time to proceed into the fight with Maleficent in her dragon form. Sora should jump to avoid her fire breath attacks, by jumping. Donald should be included in the party, ready for healing, and Beast in the party, for a strong offense. Attack with Sora's strongest magic and have strong healing items at the ready in case Donald does not help, as he will be needing his MP for other things. Keep bombarding her with your strong magic and it will be over quickly. If Sora runs out of MP, attack the dragon's head. If Beast gets knocked out, do not heal him. If Donald gets knocked out, it should be the first priority revive him immediately.
Sora also has the option of summoning Tinker Bell to restore his HP periodically—this could be a great help as Tinker Bell can bring Sora back to life once if he is drained out of HP.
Alternatively, jump and glide to the dragon's rear legs and climb onto her back. Run along the length of the beast to the base of its neck, then use Strike Raid when the head gets down to Sora's level. Chain several combos at this point. Use the "Raid" command the moment it lights up. If Sora falls off, either try to get back on, or go for her head with Ars Arcanum and other combos until the battle ends.
Jump onto the roots in the eastern corner and run to the top of them, Maleficent cannot hit while he's up here, except with her homing fire. Continually cast magic or Summon Genie. This is a slow but effective way and will keep Sora out of danger while Beast and Donald (or Goofy) pound away and keep Maleficent's attention on them.
Another strategy for this fight is to go under the large root and summon Tinker Bell. She will continually heal Sora throughout this battle, reduce the need to use Cure/Cura or an item. Let Donald and Beast do most of the work and heal them when they are hurt (it would be better if Donald has the ability Second Chance, though Goofy can use MP Gift to supply Sora with MP for healing). The only attack that the Dragon can hit Sora with when he is under the large root is the series of green blasts, which does quite a bit of damage. To prevent this from hitting him, use Guard to deflect it or Aero/Aerora/Aeroga. Finally, after the other party memebers do all the hard work, come out of the hiding place and attack continually or strike the final blow. Fortunately, Sora can cast Stop to keep the dragon frozen for about a little more than a second so Sora can deal the final blow.
An alternative strategy is to keep Donald and Goofy in the team, have Ars Arcanum equipped on Sora. Give Second Wind to both Donald and Goofy and give Goofy MP Gift. As soon as the battle begins, summon Tinker Bell as she will heal you also. Attack her head with Ars Arcanum until Sora runs out of MP. When she starts breathing fire, run away and cast Fira at her. Do not worry about MP as Goofy will keep giving his to Sora. If Donald is Knocked Out, heal him as he is the main healer. When she summons the orbs of fire, hit them away as doing so will give tech points.
An additional strategy is to glide to her back leg and jump on her back, preferably in between her wings. From here continually use the Strike Raid ability to inflict damage. The party should consist of Goofy (equipped with MP Gift) and Beast. Load these characters with Ethers so that can rejuvenate the MP Strike Raid uses. Have Sonic Blade unequipped so that Sora doesn't accidentally use it on her head and fly into Maleficent's attacks.
The Fireglow Summon gem, which allows Sora to summon Mushu, is the prize for victory.
Kingdom Hearts: Chain of Memories
In Kingdom Hearts: Chain of Memories, Sora fights Maleficent again, but only in her Dragon form. She fights similarly to her battle in Kingdom Hearts, but with more time in between attacks. When Sora fights her, the Gimmick Card creates a pile of bricks which allows him to reach her head (her only weak point) more easily. This also keeps Sora from being injured from her stomping attack. However, each stomp destroys some of the bricks.
In Re: Chain of Memories, the pile of bricks is replaced with a moving pedestal—Sora can move freely towards Maleficent's head while he is on it. Successfully breaking Maleficent's stomp attack keeps the pedestal aloft, allowing Sora to continue attacking her head. However, note that she is immune to some Sleights.
In Reverse/Rebirth, Riku fights Maleficent as well. It is basically the same fight as with Sora, but it is easier since Riku fights her at the very beginning of the game.
When Aqua fights against Maleficent's dragon form, she'll have Prince Phillip as an ally, as well as access to D-Links, Shotlocks, and Command Styles. It is important to realize that Aqua does not excel in physical attack, but she prefers to use magic to conquer foes. One should also take notice of the dragon's only weak point being its head and the fact that it only attacks the area directly in front of it. So long as a hit-and-run strategy is used, minimal damage will be received.
At the start of the battle, Aqua should immediately Cartwheel over to the dragon's side, occasionally bombarding her with Thunder, Blizzard, and Fire magic. This will eventually activate the Spell Weaver Command Style, but Aqua will not have a need for its benefits. If Aqua is too far away from the dragon, the gap can be closed with Barrier Surge or a similar attack. The Dragon may perform a biting combo, but this can be easily avoided with Cartwheel. If Aqua is in the dragon's attack range, use Mine Square and immediately Cartwheel away. As the dragon will occasionally rear back and land to create twin, short-range shockwaves, she will take heavy damage as she lands on the mines while Aqua avoids taking damage completely.
Occasionally during the battle, the dragon will breathe her signature green fire. Prince Phillip calls out to Aqua, which is the signal to get behind him (he uses his shield to completely block the flames from damaging either of them). Once the flames begin to spawn on the ground, Phillip will throw Aqua over the flames to attack the dragon once she activates the command "Selfless Prince" by pressing and then when the on-screen prompts appear which will cause Aqua to land on the dragon's head, stunning her. Aqua should then resume the hit-and-run strategy, only bombarding the dragon with magic attacks, physical attacks only when it is safe to do so. As her HP dwindles, the dragon will launch off the battlefield and begin to fly around the area. Pressing and again will allow Phillip to throw Aqua to the dragon's level, allowing a special attack to be landed.
Aqua has a strong chance of landing on the dragon's back once this attack is completed and can attack the dragon with physical attacks (such as the powerful Spell Weaver). Magic can also be used to end the battle quickly. Note that while on the Dragon's back, enough attacks will cause her to fall to the ground stunned.
An alternate strategy would be running behind Maleficent at the start of the battle. If Aqua is well equipped with magic, all she needs to do is continually attack using magic without moving from behind the dragon. Here, it is basically impossible to sustain damage. Although a slower strategy, the constant use of magic from the point of safety behind the dragon is an equally effective method to easily defeat Maleficent.